Freezing of Nonwoody Plant Tissue: II. Cell Damage and the Fine Structure of Freezing Curves

Increasing pretreatment day temperatures of 20, 30, and 40 C resulted in decreased net photosynthesis in Agropyron smithii (C₃) while in Bouteloua gracilis (C₄) net photosynthesis was increased. The effect on photosynthesis of increasing analysis temperatures was the same as observed by increasing pretreatment temperatures. Resistance of the stomata and boundary layer were less affected by pretreatment temperatures than were the remaining resistances of a physical and chemical nature. Resistances for A. smithii were increased and those for B. gracilis were decreased by increasing pretreatment temperatures. Phenology of the species in the shortgrass prairie is such that A. smithii has its greatest growth activity during the cool portion of the growth season, whereas B. gracilis is most active in the warm portion. Thus, photosynthetic adaptation to temperature is strongly suggested as a strategy for ecosystem utilization by reduction of interspecific competition.     

Field measurements of photosynthesis,water-use efficiency,and growth inAgropyron smithii (C3) andBouteloua gracilis (C4) in the Colorado shortgrass steppe

Summary Field measurements of gas exchange and growth were conducted on a C₃ grass,Agropyron smithii, and a C₄ grass,Bouteloua gracilis, in order to further establish the adaptive significance of the C₄ pathway under natural conditions. Maximum rates of leaf area expansion in tillers and maximum seasonal photosynthesis rates of both species occurred during the cool, early summer month of June. The occurrence of maximum growth and photosynthesis inB. gracilis during this cool period was apparently related to its occupation of warm microenvironments next to the ground surface. As temperatures increased during the midsummer, photosynthesis rates decreased to 47% and 55% of the seasonal maximum inB. gracilis andA. smithii, respectively. Water-use efficiencies in both species were similar or slightly higher forB. gracilis during June, the period of maximum growth. By mid-July, however, leaves of the C₃ grass,A. smithii, exhibited water-use efficiencies approximately half as high asB. gracilis. These differences in water-use efficiency were the result of differences in stomatal conductance, rather than differences in daily CO₂ uptake rates which were similar in both species. The results demonstrate that in certain environments there are no offset periods of growth and maximum photosynthesis during the growing season in these C₃ and C₄ species. The greater amounts of daily water use inA. smithii during the midsummer might contribute to its much greater abundance in lowland sites in the shortgrass steppe. The C₄ grass,B. gracilis, occurs in dry upland sites in addition to the more mesic lowland sites.     

Temperature relations of photosynthetic response in populations of Verbascum thapsus L.

Summary Seedlings representative of Verbascum thapsus L. populations from thermally diverse habitats were grown under uniform, controlled conditions. The plants were used to obtain temperature response curves for net photosynthesis over a range of 15–40°C. In general, all experimental plants exhibited similar rates of net photosynthesis at 20, 25, 30, and 35°C. Plants representative of cool habitat populations (high-latidude and high-altitude) had greatest rates of net photosynthesis at the lower temperatures and much lower rates at 40°C. Plants representative of warm habitat populations (low-latitude and low-altitude) exhibited rates of net photosynthesis at 40°C which were nearly twice those of plants representative of cool habitat populations. Carbon dioxide transfer resistances are discussed with reference to plant control of photosynthesis at different temperatures. Patterns of photosynthesis and resistance response among plants representative of different habitats suggest ecotypic variation has occurred only to a very limited extent. Therefore, the patterns exhibited by experimental plants suggest that Verbascum thapsus' success in a number of diverse sites is related to the ability of all members of the species to photosynthesize over a broad range of temperatures.     

Consequences of growth at two carbon dioxide concentrations and two temperatures for leaf gas exchange in Pascopyrum smithii (C3) and Bouteloua gracilis (C4)*

Continually rising atmospheric CO₂ concentrations and possible climatic change may cause significant changes in plant communities. This study was undertaken to investigate gas exchange in two important grass species of the short-grass steppe, Pascopyrum smithii (western wheat-grass), C₃, and Bouteloua gracilis (blue grama), C4, grown at different CO₂ concentrations and temperatures. Intact soil cores containing each species were extracted from grasslands in north-eastern Colorado, USA, placed in growth chambers, and grown at combinations of two CO₂ concentrations (350 and 700 μmol mol⁻¹) and two temperature regimes (field average and elevated by 4°C). Leaf gas exchange was measured during the second, third and fourth growth seasons. All plants exhibited higher leaf CO₂ assimilation rates (A) with increasing measurement CO₂ concentration, with greater responses being observed in the cool-season C₃ species P. smithii. Changes in the shape of intercellular CO₂ response curves of A for both species indicated photosynthetic acclimation to the different growth environments. The photosynthetic capacity of P. smithii leaves tended to be reduced in plants grown at high CO₂ concentrations, although A for plants grown and measured at 700μmol mol⁻¹ CO₂ was 41% greater than that in plants grown and measured at 350 μmol mol⁻¹ CO₂. Low leaf N concentration may have contributed to photosynthetic acclimation to CO₂. A severe reduction in photosynthetic capacity was exhibited in P. smithii plants grown long-term at elevated temperatures. As a result, the potential response of photosynthesis to CO₂ enrichment was reduced in P. smithii plants grown long-term at the higher temperature.     

PHOTOSYNTHETIC SENSITIVITY TO TEMPERATURE IN POPULATIONS OF TWO C4 BOUTELOUA (POACEAE) SPECIES NATIVE TO DIFFERENT ALTITUDES

The relationships between photosynthesis, flowering, and growth temperatures were examined experimentally in four populations of the C₄ grass genus Bouteloua. Field-collected plants were grown under two temperature regimes, cool (20 C day/6 C night) and warm (30/16), representative of the extreme populations. Populations collected from the warm climates had significantly lower photosynthetic capacity when grown in the cool chamber relative to the warm chamber, while photosynthetic capacity in the cool climate populations did not differ between the growth conditions. Additionally, exposure to a 2-day cold temperature treatment (10/-2), representative of late-season frosts in high altitude sites, resulted in further reductions in photosynthesis in the warm climate plants, but not in the cool climate plants. This effect was greater for plants grown in the cool growth chamber. Flowering was reduced by 70% in the warm climate plants grown in the cool chamber, and was correlated with photosynthetic inhibition following the short-term cold temperature treatment. These results indicate that genetic differentiation for photosynthetic temperature sensitivity has occurred in the cool climate populations, and that long-term exposure to cool temperatures coupled with short-term relatively extreme low temperatures results in greater photosynthetic inhibition in nontolerant populations.     

Temperature and salinity regulation of growth and gas exchange of Salicornia fruticosa (L.) L.

Summary Salicornia fruticosa was collected from a salt marsh on the Mediterranean sea coast in Libya. Growth and gas exchange of this C₃ species were monitered in plants pretreated at various NaCl concentrations (0, 171, 342, 513 and 855 mM). Maximum growth was at 171 mM NaCl under cool growth conditions (20/10° C) and at 342 mM NaCl under warm growth conditions (30/15° C) with minimum growth at 0 mM NaCl (control). Net photosynthesis (Pn) was greatest in plants grown in 171 mM NaCl with plants grown at 513 and 855 mM having lowest rates. Maximum Pn was at 20–25° C shoot temperatures with statistically significant reductions at 30° C in control plants while salt treated plants showed such reductions at 35° C. Salt treatments increased dark respiration over the control at 171 and 342 mM but reduced it at higher concentrations. Photorespiration was reduced by salt treatment and increased by increasing shoot temperature. Greatest transpiration was in 171 mM NaCl treated plants and increasing shoot temperature increased transpiration in all treatments. Stomatal resistance to CO₂ influx was influenced only moderately by temperature while increasing salinity resulted in increased stomatal resistance. In general both temperature and salinity increased the mesophyll resistance to CO₂ influx. The species seems adapted to the warm saline habitat along the Mediterranean sea coast, at least partially, by its ability to maintain relatively high Pn at moderate NaCl concentrations over a broad range of shoot temperatures.     

Time course of photosynthetic temperature acclimation in Carex eleocharis Bailey

Abstract Photosynthetic temperature acclimation in Carex eleocharis has been demonstrated in a previous study in which warm grown (35/15°C) plants were shown to have photosynthetic temperature optima approximately 14°C higher than cool grown (20/15°C) plants (Monson, Littlejohn & Williams, 1983). The current study examined the time course of this acclimation by determining photo-synthetic temperature optima as a function of time, of cool grown plants moved to warm growing conditions. Leaves which had developed under cool conditions were capable of an upward adjustment of 6–8°C of their optimum photosynthetic temperature within a time span of 6–14 d. For greatest photosynthetic temperature acclimation it was necessary for leaves to form and develop entirely under warm conditions. These leaves exhibited a 14–15°C upward adjustment of their optimum temperature for photosynthesis within 20–31 d since moving plants from cool to warm growing conditions. Thus, the time course of this acclimation is of short enough duration to be significant during the growing season and presumably contributes toward the ability of this species to maintain active growth during the cool and warm portions of the growing season. It is also noted that the plant with its capacity to form new leaves, has a much wider acclimation capacity than any single leaf.     

The subdominant status of Echinocereus viridiflorus and Mammillaria vivipara in the shortgrass prairie: The role of temperature and water effects on gas exchange

Summary The subdominant CAM species, Echinocereus viridiflorus and Mammillaria vivipara, collected from the shortgrass prairie in northeastern Colorado were pretreated and analyzed for gas exchange under cool temperatures (20/15°C) and warm temperatures (35/15°C). Well watered plants of both species under a 35/15°C thermoperiod fixed atmospheric CO₂ during the night and early moring. Echinocereus viridiflorus grown and analyzed at 20/15°C fixed CO₂ during the night, early morning and late afternoon but total carbon gain over a 24 h period is less than when grown and analyzed under the 35/15°C thermoperiod. Mammillaria vivipara grown and analyzed at 20/15°C assimilates CO₂ at low rates during all parts of a 24 h period with the greatest CO₂ fixation rates occuring from midday to late afternoon. The total carbon gain under the 20/15°C thermoperiod is less than that for this species under the 35/15°C thermoperiod. Decreasing the night temperature of plants grown under the warm conditions to 10°C or 5°C results in a depression of the night CO₂ fixation in both species. E. viridiflorus from the cool growth conditions showed an enhancement of the CO₂ uptake during the night, early morning and late afternoon when subjected to the cooler night temperatures (10°C and 5°C). The CO₂ uptake of M. vivipara grown at 20/15°C shows an enhancement during the night and early morning while the CO₂ fixation during midday and late afternoon is slightly depressed under cool night temperatures (10° and 5°C). Under the 35/15°C thermoperiod both species exhibit depressed rates of CO₂ fixation during the night and early morning when water stressed. Plants of both species grown under the 20/15°C thermoperiod exhibit no net CO₂ fixation following five weeks of water deprivation. Upon rewatering, E. viridiflorus begins to recover its capacity for CO₂ fixation within 24 h under both the warm and cool temperature regimes. However, M. vivipara did not show recovery within 48 h following rewatering under the warm or cool temperature regime. Contrasting the patterns of gas exchange of the subdominant species, E. viridiflorus and M. vivipara, with a dominant CAM species of the shortgrass prairie, Opuntia polyacantha reveals significant differences that may well dictate the role of these species in this ecosystem. E. viridiflorus and M. vivipara have a lower capacity of carbon gain and recovery from water stress than O. polyacantha mainly due to their lack of late afternoon CO₂ uptake. This study suggests that carbon gain plays an important role in limiting E. viridiflorus and M. vivipara in the shortgrass prairie ecosystem.     

Gas Exchange and Carbohydrate and Nitrogen Concentrations in Leaves of Pascopyrum smithii (C3) and Bouteloua gracilis (C4) at Different Carbon Dioxide Concentrations and Temperatures

Pascopyrum smithii (C₃) andBouteloua gracilis (C₄) are importantforage grasses native to the Colorado shortgrass steppe. Thisstudy investigated photosynthetic responses of these grassesto long-term CO₂enrichment and temperature in relation to leafnonstructural carbohydrate (TNC) and [N]. Glasshouse-grown seedlingswere transferred to growth chambers and grown for 49 d at twoCO₂concentrations (380 and 750 µmol mol^-1) at 20 and 35°C, and two additional temperatures (25 and 30 °C) at750 µmol mol^-1CO₂. Leaf CO₂exchange rate (CER) was measuredat a plant's respective growth temperature and at two CO₂concentrationsof approx. 380 and 700 µmol mol^-1. Long-term CO₂enrichmentstimulated CER in both species, although the response was greaterin the C₃,P. smithii . Doubling the [CO₂] from 380 to 750 µmolmol^-1stimulated CER ofP. smithii slightly more in plants grownand measured at 30 °C compared to plants grown at 20, 25or 35 °C. CO₂-enriched plants sometimes exhibited lowerCER when compared to ambient-grown controls measured at thesame [CO₂], indicating photosynthetic acclimation to CO₂growthregime. InP. smithii , such reductions in CER were associatedwith increases in TNC and specific leaf mass, reductions inleaf [N] and, in one instance, a reduction in leaf conductancecompared to controls. InB. gracilis , photosynthetic acclimationwas observed more often, but significant changes in leaf metabolitelevels from growth at different [CO₂] were generally less evident.Temperatures considered optimal for growth (C₃: 20 °C; C₄:35 °C) sometimes led to CO₂-induced accumulations of TNCin both species, with starch accumulating in the leaves of bothspecies, and fructans accumulating only inP. smithii. Photosynthesisof both species is likely to be enhanced in future CO₂-enrichedand warmer environments, although responses will sometimes beattenuated by acclimation. Acclimation; blue grama (Bouteloua gracilis (H.B.K.) Lag ex Steud.); leaf nitrogen concentration; nonstructural carbohydrates; photosynthesis; western wheatgrass (Pascopyrum smithii (Rydb.) Love)     

The quantum yield for CO2 uptake in C3 and C4 grasses

The quantum yield for CO₂ uptake was measured in C₃ and C₄ monocot species from several different grassland habitats. When the quantum yield was measured in the presence of 21% O₂ and 340 cm³ m^-3 CO₂, values were very similar in C₃ monocots, C₃ dicots, and C₄ monocots (0.045–0.056 mole CO₂ · mole^-1 quanta absorbed). In the presence of 2% O₂ and 800 cm³ m^-3 CO₂, enhancements of the quantum yield values occurred for the C₃ plants (both monocots and dicots), but not for C₄ monocots. A dependence of the quantum yield on leaf temperature was observed in the C₃ grass, Agropyron smithii, but not in the C₄ grass, Bouteloua gracilis, in 21% O₂ and 340 cm³ m^-3 CO₂. At leaf temperatures between 22–25°C the quantum yield values were approximately equal in the two species.     

GRAZING HISTORY,DEFOLIATION, AND FREQUENCY-DEPENDENT COMPETITION: EFFECTS ON TWO NORTH AMERICAN GRASSES

Agropyron smithii and Bouteloua gracilis plants from intensively grazed prairie dog colonies and from a grazing exclosure in Wind Cave National Park, South Dakota, were used to compare responses of conspecific populations with different histories of exposure to grazing and to competition for light. In separate experiments for each species, plants grown in monocultures and two-population replacement-series mixtures were used to examine effects of defoliation, frequency-dependent competition, and population on biomass and morphology. Colony and exclosure plants frequently responded differently. Defoliation more often adversely affected exclosure plants than colony plants, while interpopulation competition more often adversely affected colony plants. Defoliation frequently negated the competitive advantage of exclosure plants. Intrapopulation competition appeared to be greater among exclosure than colony plants. Our results indicate that conclusions based on studies of plants in long-term exclosures may not apply to plant populations having long histories of intensive grazing. While there were differences between species, in both, these experiments provide evidence of population differentiation, resulting in morphologically dissimilar populations which responded differently to defoliation and to inter- and intrapopulation competition.     

Thermoregulatory behavior of the triggerfish Balistes fuscus in an electronic shuttlebox

Ten blue triggerfish,Balistes fuscus, were tested individually for 3 days each in Ichthyotron electronic shuttleboxes to measure their thermoregulatory behavior. The modal thermal preferendum, a species-specific measure of temperature preference which is independent of prior thermal acclimation, was 25 °C. The triggerfish voluntarily occupied a 16–27 °C range of temperature, out of a potentially available range of 0–50 °C. There was no significant difference in preferred temperature between night and day, indicating lack of a thermoregulatory rhythm in this species. The preferred temperature range of this tropical marine reef species is similar to that of cool temperate freshwater and marine fishes; many warm temperate species prefer higher temperatures.     

The ratio of germanium to silicon in plant phytoliths: quantification of biological discrimination under controlled experimental conditions

Slight differences in the chemical behavior of germanium (Ge) and silicon (Si) during soil weathering enable Ge/Si ratios to be used as a tracer of Si pathways. Mineral weathering and biogenic silicon cycling are the primary modifiers of Ge/Si ratios, but knowledge of the biogenic cycling component is based on relatively few studies. We conducted two sets of greenhouse experiments in order to better quantify the range and variability in Ge discrimination by plants. Graminoid species commonly found in North American grassland systems, Agropyron smithii, Schizachyrium scoparium, and Andropogon gerardii were grown under controlled hydroponic environmental conditions. Silicon leaf contents were positively correlated with solution Si and ambient temperature but not with nutrient solution pH, electrical conductivity, or species. The Ge/Si ratio incorporated into phytoliths shows a distribution coefficient [(Ge/Si)_phytolith/(Ge/Si)_solution] of about 0.2 and is remarkably invariant between species, photosynthetic pathway, and solution temperature. Ge seems to be discriminated against during the uptake and translocation of Si to the opal deposition sites by about a factor of five. In the second experiment, a wider range of graminoid species (Agropyron smithii, Bouteloua gracilis, Buchloe dactyloides, Oryzopsis hymenoides, Schizachyrium scoparium and Andropogon gerardii) were grown in two different soil mediums. Plant phytoliths showed a distribution factor of about 0.4 for field grown grasses, and 0.6 for potting soil grown grasses with no clear trends among the species. Evidence of the direction and degree of biological Ge discrimination during plant uptake provides a geochemical finger print for plants and improves the utility of Ge/Si ratios in studies of terrestrial weathering and links between Si cycles in terrestrial and marine systems.     

Acclimation of photosynthesis to temperature in eight cool and warm climate herbaceous C3 species: Temperature dependence of parameters of a biochemical photosynthesis model

To determine how parameters of a Farquhar-type photosynthesis model varied with measurement temperature and with growth temperature, eight cool and warm climate herbaceous crop and weed species were grown at 15 and 25 °C and single leaf carbon dioxide and water vapor exchange rates were measured over the range of 15 – 35 °C. Photosynthetic parameters examined were the initial slope of the response of assimilation rate (A) to substomatal carbon dioxide concentration (C_i), A at high C_i, and stomatal conductance. The first two measurements allow calculation of V_Cmax, the maximum rate of carboxylation of ribulose bisphosphate carboxylase and J_max, the maximum rate of photosynthetic electron transport, of Farquhar-type photosynthesis models. In all species, stomatal conductance increased exponentially with temperature over the whole range of 15 – 35 °C, even when A decreased at high measurement temperature. There were larger increases in conductance over this temperature range in the warm climate species (4.3 ×) than in the cool climate species (2.5 ×). The initial slope of A vs. C_i exhibited an optimum temperature which ranged from 20 to 30 °C. There was a larger increase in the optimum temperature of the initial slope at the warmer growth temperature in the cool climate species than in the warm climate species. The optimum temperature for A at high C_i ranged from 25 to 30 °C among species, but changed little with growth temperature. The absolute values of both the initial slope of A vs. C_i and A at high C_i were increased about 10% by growth at the warmer temperature in the warm climate species, and decreased about 20% in the cool climate species. The ratio of J_max — V_Cmax normalized to 20 °C varied by more than a factor of 2 across species and growth temperatures, but differences in the temperature response of photosynthesis were more related to variation in the temperature dependencies of J_max and V_Cmax than to the ratio of their normalized values.This revised version was published online in October 2005 with corrections to the Cover Date.     

Distribution of range and cultivated grassland plants in southern Alberta

We analysed the geographic distribution of native grassland and introduced grassland plants and the association of species abundance with climate and site characteristics in southern Alberta using a database of range and pasture assessments collected during 1991, 1992 and 1993. Distribution maps of native and introduced grassland plants could be inferred from association between site data recording botanical composition or presence and mean monthly climate surfaces for May and August. Introduced species formed three main geographical patterns with alfalfa, smooth bromegrass and crested wheatgrass most widespread, Russian wildrye restricted to the south eastern quarter and timothy, creeping red fescue, bluegrass and clovers restricted to the northern half. Native plants formed four main patterns characterised by Stipa comata and Bouteloua gracilis – south eastern; Agropyron spp. – widespread; Festuca spp. – northern and foothills; and Stipa viridula – sparse. Relative abundance of Stipa comata and Bouteloua gracilis were related primarily to latitude and longitude and variables describing temperature during the growing season. Biomass increased and range condition decreased with increasing latitude reflecting the decline in dominant native species, the increase in introduced and invader species and the better growing season moisture in northern areas. The maps provide a recent snapshot of the condition of commercially utilised native and cultivated grasslands in Alberta. They constitute a valuable reference point for comparison with future climate or management-induced change.     

Plant morphology and grazing history:

Grazing-related, intraspecific, morphological variation was studied in four North American grasses (Bouteloua gracilis, Agropyron smithii, Schizachyrium scoparium, and Andropogon gerardii) from eight locales in Wind Cave National Park, South Dakota: three locales currently occupied and heavily grazed by prairie dogs (Cynomys ludovicianus), colonized (since settlement) for 2–100 years, where native ungulates concentrate grazing activities; an extinct colony locale from which prairie dogs were removed 30 years previously, moderately to lightly grazed by ungulates; two noncolony locales, moderately to lightly grazed by ungulates; and two locales from within a 50-year-old grazing exclosure, with no known history of grazing by prairie dogs nor any recent grazing by ungulates. Data were collected both in situ and in common environments.Active-colony plants were more frequently and more heavily grazed than those at other grazed locales. In situ, plants from heavily grazed populations were smaller and more prostrate than those from populations with little or no grazing (including the extinct colony) and interpopulation variation corresponded to current grazer use. After several growing seasons in common environments, there were still significant interpopulation differences; however, variation often corresponded with grazing history. Although differences between active-colony and noncolony plants were somewhat reduced (indicating some phenotypic plasticity), active-colony plants were still smaller and more prostrate. However, extinct-colony plants more closely resembled active-colony plants than noncolony plants. Morphological variation among these populations is the result of more than simple grazer use; historical factors and the dynamic nature of the grazing regimes are also contributing factors.Abbreviations A. gerardii Andropogon gerardii - A. smithii Agropyron smithii - BFC Bison Flats colony locale - BFN noncolony locale at Bison Flats - B. gracilis Bouteloua gracilis - EXT Upper Highland extinct-colony locale - GDN common garden - GH greenhouse - NEW new satellite colony locale - PVC Pringle Valley colony locale - PVN noncolony locale in Pringle Valley - S. scoparium Schizachyrium scoparium - WCNP Wind Cave National Park, South Dakota, USA - XFN exclosure locale just inside exclosure fence from BFN - XHQ exclosure locale near headquarters buildings     

Growth and Partitioning in Pascopyrum smithii (C3) and Bouteloua gracilis(C4) as Influenced by Carbon Dioxide and Temperature

This study investigated how CO₂and temperature affect dry weight(d.wt) accumulation, total nonstructural carbohydrate (TNC)concentration, and partitioning of C and N among organs of twoimportant grasses of the shortgrass steppe,Pascopyrum smithiiRydb. (C₃) andBouteloua gracilis(H.B.K.) Lag. ex Steud. (C₄).Treatment combinations comprised two temperatures (20 and 35°C)at two concentrations of CO₂(380 and 750 µmol mol^-1),and two additional temperatures of 25 and 30°C at 750 µmolmol^-1CO₂. Plants were maintained under favourable nutrient andsoil moisture and harvested following 21, 35, and 49d of treatment.CO₂-induced growth enhancements were greatest at temperaturesconsidered favourable for growth of these grasses. Comparedto growth at 380 µmol mol^-1CO₂, final d.wt of CO₂-enrichedP.smithiiincreased 84% at 20°C, but only 4% at 35°C. Finald.wt ofB. graciliswas unaffected by CO₂at 20°C, but wasenhanced by 28% at 35°C. Root:shoot ratios remained relativelyconstant across CO₂levels, but increased inP. smithiiwith reductionin temperature. These partitioning results were adequately explainedby the theory of balanced root and shoot activity. Favourablegrowth temperatures led to CO₂-induced accumulations of TNCin leaves of both species, and in stems ofP. smithii, whichgenerally reflected responses of above-ground d.wt partitioningto CO₂. However, CO₂-induced decreases in plant tissue N concentrationswere more evident forP. smithii. Roots of CO₂-enrichedP. smithiihadgreater total N content at 20°C, an allocation of N below-groundthat may be an especially important adaptation for C₃plants.Tissue N contents ofB. graciliswere unaffected by CO₂. Resultssuggest CO₂enrichment may lead to reduced N requirements forgrowth in C₃plants and lower shoot N concentration, especiallyat favourable growth temperatures. Acclimation to CO₂; blue grama; Bouteloua gracilis ; carbohydrate; climate change; global change; grass; growth; growth temperature optima; nitrogen; N uptake; Pascopyrum smithii; western wheatgrass     

Rhizosphere microorganism effects on soluble amino acids,sugars and organic acids in the root zone ofAgropyron cristatum,A. smithii andBouteloua gracilis

Three axenic and rhizosphere microorganism-inoculated shortgrass steppe plant species were evaluated for possible differences in residual organic carbon and nitrogen present as sugars, organic acids and amino acids. IntroducedAgropyron cristatum was compared toA. smithii andBouteloua gracilis, which are dominant species in the native shortgrass steppe. These plants, grown for 90 days in root growth chambers, showed differences in residual organic carbon and nitrogen per gram of root, and rhizosphere microbe presence resulted in additional changes in these compounds. The root biomass ofB. gracilis was significantly increased with microbes present. TheAgropyron species had significantly lower amino acid levels with microbes present, while under the same conditions, theB. gracilis showed significant decreases in residual sugars. Based on the amino acids, sugars and organic acids, the C/N ratio of the sterileA. cristatum was higher than forB. gracilis. Rhizosphere microbe presence did not result in changes in these C/N ratios. These results suggest thatA. cristatum, with microbes present, will have lower levels of amino acids present, whileB. gracilis, with a lower C/N ratio, will have sugars used to a greater extent by the rhizosphere microbes. This resulted in the higher levels of residual soluble organic C and N in the rhizosphere ofB. gracilis, in comparison with the introducedA. cristatum. These differences may be critical in influencing the course of nutrient accumulation and plant competition in short-grass steppe communities, and in understanding basic aspects of plant-rhizosphere microorganism interactions.     

The response of mycorrhizal colonization to elevated CO2 and climate change in Pascopyrum smithii and Bouteloua gracilis

Large intact soil cores of nearly pure stands of Pascopyrum smithii (western wheatgrass, C₃) and Bouteloua gracilis (blue grama, C₄) were extracted from the Central Plains Experimental Range in northeastern Colorado, USA and transferred to controlled environment chambers. Cores were exposed to a variety of water, temperature and CO₂ regimes for a total of four annual growth cycles. Root subsamples were harvested after the completion of the second and fourth growth cycles at a time corresponding to late winter, and were examined microscopically for the presence of mycorrhizae. After two growth cycles in the growth chambers, 54% of the root length was colonized in P. smithii, compared to 35% in blue grama. Field control plants had significantly lower colonization. Elevation of CO₂ increased mycorrhizal colonization in B. gracilis by 46% but had no effect in P. smithii. Temperatures 4° C higher than normal decreased colonization in P. smithii by 15%. Increased annual precipitation decreased colonization in both species. Simulated climate change conditions of elevated CO₂, elevated temperature and lowered precipitation decreased colonization in P. smithii but had less effect on B. gracilis. After four growth cycles in P. smithii, trends of treatments remained similar, but overall colonization rate decreased.     

Cultivation and carrageenan yield and quality ofKappaphycus alvarezii in the waters of Vietnam

The carrageenan-producing red algaKappaphycus alvarezii (Doty) Doty was brought to Vietnam from Japan in 1993. Branch fragments of this species were cultivated in a pond, lagoon, inlet and offshore in Vietnam for the first time. The best daily growth rate (DGR) of plants grown in the lagoon area attained 9–11 % day^–1 in May to June (cold season). The water temperature and salinity in this area ranged from 27.2–32.4 °C and 31.4–33.7 °C, respectively. DGR of plants grown in the inlet ranged from 7 to 9% day^–1 in June. Grazing by fish has been observed to occur in this area. The DGR of plants grown in the pond ranged from 5–6% in January–July, but decreased to less than 4% day^–1 in August (hot season). K. alvarezii in Vietnam showed a carrageenan yield of 18.8–24.6% and gel strength of 1566–1712 g cm^–2. These values are similar ones obtained fromK. alvarezii cultivated in the Philippines and Indonesia.